Extending an F-Curve in a certain channel
If you select a point of the F curve you can read its values on the view tab on the right of the curves window (just under modifiers).
I'm assuming that your first keyframe you want to copy is frame 3, value 0.7, and the last is frame 65, value - 2.3.
So you want to copy the curve with an offset of 63 frames on X and a value of 3 on Y.
So select the curve points, shift D to duplicate, X to move on X axis, 63, Enter.
Then Press G, Y, - 3 Enter.
Then you'll have to globally adjust the Y values of the copied keyframes to compensate the needed little movement between frame 65 and 66.